Ultrafast energy transfer and population buildup among strongly coupled and curve crossing regions of the boron oxide A (2)Pi and X (2)Sigma(+) states

Boron oxide A (2)Pi -X(2)Sigma (+) chemiluminescence resulting from the rea ction of boron atoms with nitrogen dioxide (NO2) and ozone (O-3) has been s tudied. The reactions are characterized from 10(-5) to 10(-3) Torr and at P -total similar to 1 Torr in order to assess rapid X --> A intramolecular vi brational-to-electronic transfers including BO (X(2)Sigma (+), v " = 17) M --> BO (A (2)Pi (1/2), v' = 4) + M where M = NO2, O-3 or a combination of these oxidants with argon, and the nature of the pressure dependent popula tion buildup due to a possible bottleneck associated with the curve crossin g of the BO X(2)Sigma (+) and A (2)Pi states between v' = 8 and 9 A (2)Pi. At the very lowest pressures, the B + NO2 reaction also yields emission cor responding to the BO2 A (2)Pi (u)-X(2)Sigma (+)(g) band system, however, th e B-O-3 reaction results only in BO* A-X emission and produces neither BO2 A-X nor BO B-X emission. At elevated pressures both the B-NO2 and B-O-3 sys tems yield BO2 A-X where the excited BO2 is formed in a two-step reaction s equence. The effects of ultrafast intramolecular energy transfer, manifest at pressures as low as 2 x 10(-5) Torr for the B-NO2 system, are consistent with expectations based on long-range interactions. For both the B-NO2 and B-O-3 metatheses, the BO* A (2)Pi vibrational distributions are strongly i nfluenced by (1) a combination of population buildup in vibrational levels v' greater than or equal to 9 in the vicinity of the A (2)Pi -X(2)Sigma (+) curve crossing region and (2) near resonant energy transfer among nearly i soergic levels of the X(2)Sigma (+) and A (2)Pi states (both (2)Pi (1/2) an d (2)Pi (3/2) components). The effects observed in BO demonstrate the inter action of a highly vibrationally excited ground state molecule in the prese nce of a collision partner with a cross-section well in excess of that expe ctedfor gas kinetic interaction and a rate constant exceeding 10(10) Torrs( -1). (C) 2001 Elsevier Science B.V. All rights reserved.